Clinicopathological Characteristics of Well-differentiated Papillary Mesothelioma of The Peritoneum: A Single-institutional Experience of 12 Cases

BACKGROUND/AIM: Well-differentiated papillary mesothelioma (WDPM) is histologically characterized by papillary architecture with fibrovascular cores, lined by bland mesothelial cells. We recently experienced a case of WDPM associated with multiple peritoneal inclusion cysts, which prompted us to initiate a comprehensive review of previously diagnosed WDPM cases. MATERIALS AND METHODS: The clinicopathological characteristics and immunophenotype of 12 cases of peritoneal WDPM were investigated using a review of electronic medical records, pathological examination, and immunostaining. RESULTS: The patients' ages ranged from 23 to 75 years. No patient had endometriosis or a previous history of asbestos exposure. Ten tumors were detected incidentally during surgery for other causes. Most tumors appeared as a small, single nodule on the peritoneal surface, but in three cases, WDPM presented as multiple lesions. All but one patient had no symptoms. All the patients examined are still well without postoperative recurrence. Histologically, all cases demonstrated typical papillary architecture with fibrovascular cores. The mesothelial cells lining the papillae consisted mostly of single row of cells, although areas of proliferation to multiple layers were observed in a few cases. Their nuclei appeared bland, but two cases exhibited mild nuclear atypia and prominent nucleoli. Immunostaining revealed that the mesothelial cells were positive for D2-40, cytokeratin 5/6, cytokeratin 7, and Wilms' tumor 1. CONCLUSION: We herein demonstrated the clinicopathological characteristics of peritoneal WDPMs. WDPM has distinct pathological features. Although all cases we examined were uneventful after surgery, further surveillance is recommended since the biological behavior of WDPM is still uncertain.